[Solved] Total internal reflection, underwater light? 1. The problem statement, all variables and given/known data A point source of light is at the bottom of a koi pond, at a depth of 0.525 meters. What is the radius of the circle of light formed on the water's surface? Take the index of refraction of water to be 1.33. Hint: Some of the light emitted experiences total internal reflection inside the water. 2. Relevant equations sin(crit angle) = n2/n1 n1>n2 n for air = 1.00 n for water = 1.33 3. The attempt at a solution So the critical angle for water to air is: arcsin(1/1.33) = 48.7534666 degrees This is where it all ends. There is no formula for distance or light radius. I am completely stuck at this point and cannot find anywhere in my book where I could derive the answer. I would deeply appreciate some help with this one!